The present invention relates to a method of detecting a structure in a field, said method comprising: providing an image of the field, analysing the image to obtain texture information, assigning to a plurality of areas of the image probability-values reflecting the likelihood that the respective area relates to a specific structure. Further the present invention relates to a method of steering an agricultural vehicle or implement in relation to a structure in a field, and to an agricultural vehicle comprising a steering system providing steering signals, said steering system comprising an imaging device for imaging surroundings of the vehicle and an image processing device.
Within agriculture many processes are performed on a field whereby an implement is driven in the field back and forth or around and around to cover the entire field, e.g. when ploughing, sowing or drilling, harvesting and collecting crops. In many of these processes a track is followed, said track being provided by different areas of the field exhibiting different structure with different visual texture. The different structures may e.g. be ploughed and unploughed soil, sown and non-sown areas, drilled rows and a harrowed seedbed, standing crop and lying crop or harvested ground, swaths of cut crop and harvested ground, etc.
It is a wish to be able to automate the steering of the implement and the vehicle carrying or towing the implement, and many methods are being explored for identifying tracks to be follow, like the tracks mentioned above. Such methods include methods using laser scanners, photogrammetry, etc. These methods may be combined with other methods for navigating an agricultural vehicle, such as methods based on GPS, odometry, etc.
Methods using photogrammetry include methods using stereo-photogrammetry e.g. for detecting a three-dimensional structure on the field. Such structure could be a swath of harvested crop lying on the field to be pick-up e.g. by a baler. Such stereo-photogrammetry method is e.g. known from WO-A-2007/031093, which relates to a method of controlling a baler based on 3D imaging technology.
Alternative or supplementary to stereo-photogrammetry an image of the field may be analysed to distinguish the different structures e.g. by their (visual) texture. By texture should be understood local variations due to differenced in colour, structure, such as straws standing or lying, being long or short, soil broken into smaller or larger lumps, etc.
Examples of methods using analysis of texture for distinguishing structures in an agricultural field are known, e.g.:
U.S. Pat. No. 6,336,051 discloses tracking a crop line between cut and uncut crop in a field or between a processed and an unprocessed surface of the field by analysing an image of the field by scanning the pixels of a part of the image line by line and assigning by means of a colour or a texture discriminator a value to the respective pixels. For each line a step function is fitted to determine the position of the crop line, where by a binary signal is outputted. For each line the step function thus established is compared to a predetermined step function and if the established step function is outside limits the line is labelled “after end of row”, otherwise the line is labelled “before end of row”, By counting from the top of the image an end-of-row position is established. Further a combined probability density function for processed and unprocessed surface is provided and for regions of 10×10 pixels the probability of the region belonging to the processed or unprocessed surface of the field is calculated. If the probability falls below a threshold value the region is assumed to represent an obstacle.
U.S. Pat. No. 7,400,957 discloses a method of detecting a structure in a field as mentioned above in the opening paragraph. More specifically it discloses detection of a swath of cut crop lying on a field by analysing an image, whereby pixel by pixel of the image is appointed a likelihood value based on the surrounding texture, the pixels are appointed the value swath or not swath according to a threshold value for the likelihood, thus providing a binary information whether the particular pixels are to be assigned to the swath of cut crop or not. The binary image thus provided is treated to reduce noise and the position and axes of inertia of the swath are established as a basis for providing a steering signal for a vehicle carrying the camera providing the image.